A typical switching regulator, such as a Buck converter, employs a high-side metal oxide semiconductor field effect transistor (MOSFET) and a low-side MOSFET in a push-pull configuration to generate an output current for a load. The typical Buck converter further includes a driver circuit to drive the gates of the high- and low-side MOSFETs to generate the output current for the load. A pulse width modulator (PWM) is typically employed to control the driver circuit. The PWM is generally responsive to an output feedback voltage in order to generate the proper control signal to maintain the output voltage of the Buck converter within specification.
In many cases, the load at the output of the Buck converter is unknown, particularly when the converter is initially turned on. In some cases, the load may be significantly large, such as when a deep short is present at the output of the Buck converter. If the Buck converter delivers the full or large output voltage to such a load, the resulting large current may cause damage to the MOSFETs and other components of the converter. Often, the Buck converter includes a soft-start circuitry in order to monotonically increase the output voltage of the Buck converter from approximately zero (0) Volt to a specified output voltage during start-up of the converter. If a large load is present, the ramping output voltage generally eliminates the large initial current, and the Buck converter can be turned off when the current exceeds a predetermined level.
The typical Buck converter monitors the output current only during the time that the low-side MOSFET is conducting. However, these Buck converters are generally not able to limit the instantaneous output current to the predetermined maximum level when the converter is exposed to a deep output short circuit. This happens because the converter output voltage collapses, and the controller regulation loop commands a maximum duty cycle for the high-side MOSFET, with no possibility to limit the current peak during this cycle since the current is monitored only during the time that the low-side MOSFET is conducting. Accordingly, the potential large current during the time when the high-side MOSFET is turned on can cause damage to the MOSFETs and other components of the Buck converter.